Speed control system for railroad trains



March 17, 1970 D. w. AIKEN SPEED CONTROL SYSTEM FOR RAILROAD TRAINS 3 Sheets-Sheet 1 Filed Dec. 30. 1968 Illy .@@DMSQNN @QS March 17, 1970 D. w. AIKEN SPEED CONTROL SYSTEM FOR RAILROAD TRAINS March 17, 1970 D. w. AIKEN 3,501,629

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f/Vl/ZWTUH r YWMWW United States Patent Ol 3,501,629 SPEED CONTROL SYSTEM FOR RAILROAD TRAINS Donald W. Aiken, Suffolk, N.Y., assigner to Westinghouse Air Brake Company, Swissvale, Pa., a corporation of Pennsylvania Filed Dec. 30, 1968, Ser. No. 787,787 Int. Cl. B611 23/16, 3/20 U.S. Cl. 246-34 8 Claims ABSTRACT OF THE DISCLOSURE A cab signal/speed control system for railroads with signaling blocks established from station to station. A plurality of speed limits are predetermined in accordance with known braking characteristics of the trains, each speed limit being preselected in accordance with the maximum -stopping distance required by a train having such braking characteristics when traveling at that allowed speed. Train positions are detected by audio frequency track circuits which divide each signaling block into short detector track sections. Speed selection logic circuitry selects one of the predetermined speed limit signals for transmission to an approaching train, in accordance with the detected positions of the preceding and approaching trains, such that the approaching train may be stopped from that speed within the minimum indicated spacing between trains.

My invention pertains to speed control systems for railroad trains. More specifically, this invention pertains to a system for transmitting speed limit signals through the rails of a track to a train, such signals being selected both in accordance with the detected positions of that train and the preceding train and also in accordance with the established braking characteristics of such trains.

One problem in the operation of rapid transit systems, or heavily traveled railroad commuter services, is the maintenance of close headway between trains at station stops during rush hours, such close headway operation being one of the more efficient solutions to furnishing a high capacity commuter service. This problem increases where high average speed of the trains is also a goal of the operation. It is generally accepted that close headway can scarcely be maintained without cab signal or speed control systems functioning in the stretch of track over which the trains operate. When standardized train or multipleunit car sets are used in such operations, the known braking characteristics, established by the design of the equipment, may be incorporated into the signaling system design to further assist in maintaining close headway. This incorporation of the braking characteristics is accomplished by considering the known braking distances from various operating speed limits when establishing the allowable speeds for following trains under various conditions of train spacing. The speed selection logic is then designed to select such predetermined speeds in accordance with the detected positions of the trains, that is, the existing spacing condition. In other words, the maximum allowed speed for a following train is selected so that it is known that the train may be stopped from that speed within the minimum space available between it and the immediately preceding train.

Accordingly, it is an object of my invention to provide an improved cab signal system for trains incorporating the designed braking characteristics of those trains into the predetermined speed signal selections.

Another object of my invention is a cab signal and/or speed control system for railroad trains in which the allowed speeds for following trains under different condi- Patented Mar. 17, 1970 lCe tions of train spacing are predetermined from the train braking characteristics.

Still another object of my invention is a cab signal or speed control system for railroad trains in which the train detection sections are greater in number than the cab signal blocks so that cab signal selections may vary within an established block in accordance with train positions.

It is also an object of my invention to provide an irnproved speed control system for railroads utilizing station to station blocks for the transmission of speed limit signals to the trains, such speed limits being predetermined in accordance with the established braking characteristics of those trains and the specific selections of transmitted speed limits being in accordance with the detected train position within such station to station blocks.

Still another object of my invention is a speed signaling system for a stretch of railroad track, with the application of speed signals by station to station block and with train detection in accordance with shorter track sections within such blocks, in which the selective application of speed signals in the block, from a plurality of speed limits predetermined in accordance with the braking characteristics of the trains, is in accordance with detected positions of an approaching train and the next preceding train.

Other objects, features, and advantages of my invention will become apparent from the following specification and claims when taken in connection with the accompanying drawings.

Systems embodying the arrangement of my invention are preferably, although not exclusively, applied to stretches of railroad with relatively closely spaced passenger stations, with trains normally stopping at each station. This definition, of course, applies also to rail rapid transit systems. In practicing my invention, I apply cab signaling or speed signaling control energy to the rails of the track stretches generally by station to station block. My invention is not so limited to this specific type of application of cab/speed signal energy, but is thus specifically shown for purposes of the present description. A cab signal transmitter is thus located at a point at which trains enter each station platform area and supplies its output energy into the approach block. Throughout this specification, the term approac is used in the conventional manner, that is, as applying to that stretch of track through which a train approaches a specific location or signal position. Conversely, the term advance where used in this description applies to that portion of the track through which a train departs or recedes from the particular transmitter location or signal position.

Each cab signal block is divided into detector track sections, shown speciically as three sections per block although, of course, not so limited in the overall application of my invention. Each such section is provided with a track circuit to continuously detect the presence or Iabsence of trains within that section. In the two forms illustrated, these track circuit arrangements are specifically shown as audio frequency (AF) track circuits with a plurality of receivers responsive to, land located in each direction from, a single AF transmitter. In one form, this AF track -circuit arrangement extends throughout the approach station to station block and also includes an overlap into the advance station to station block to provide additional train position detection for special purposes in the arrangement of' my invention. In each form, the AF circuit transmitter is collocated with the cab signal transmitter, the units being connected to the rails in multiple. The AF receivers are then connected across the rails at selected points to establish the shorter track sections for train detection. The train detection information, both for the approach and the advance signaling blocks, is consolidated, by means of `wayside line wires, at each cab signal transmitter location. At this central location, logic circuits are used to receive the train detection information and select a proper speed for an approaching train, controlling the cab signal o1' speed signal transmitter accordingly. This speed selection, from a variety of speed limits predetermine in accordance with established 'braking characteristics and the track section lengths, is specifically made in accordance with the spacing between trains as indicated by the detected locations of the approaching train and the immediately preceding train.

I shall now describe my invention in more specific detail referring from time to time to the accompanying drawings in which:

FIG. l is a schematic illustration of the apparatus associated with a stretch of railroad track to provide a speed signaling system embodying one form of my invention.

FIG. 2 is a similar schematic showing of the same stretch of railroad track with a slightly modified arrangement of speed signaling apparatus embodying a second form of the invention.

FIG. 3 is a speed limit selection chart f-or the stretch of track suitable for and characteristic of the operation of the signaling system shown in FIG. 1.

A similar chart is shown in FIG. 4 illustrating speed limit selections which may be associated with the apparatus arrangement of FIG. 2.

In each of the drawings, similar items of the apparatus are designated by identical symbols and reference characters. As will be more fully explained, conventional symbols are used to designate apparatus for which any one of several standard items may be used and in which the specific details of the apparatus are not a unique part of the system of my invention.

Reference is now made to FIG. 1 as background for the following specific description of the apparatus and its operation. Across the top of this drawing is a representation of a stretch of railroad track, shown by a double line designated by the references 11 and 12. This stretch of track is divided into detector track sections numbered 1 to 7 consecutively in the direction of normal train movement, which is from right to left as illustrated by the arrow shown in the upper right of the drawing. The division of the stretch into detector sections is conventionally indicated by dotted lines, connected between the double line track illustration, which also designate in a very conventional manner the rail connections of the specific apparatus at such points. Although these track sections are shown as relatively equal in length for convenience in the description, this is not a specific requirement of my system. Rather, in some installations, better operation results if sections are not of equal length in accordance with the position and procedure of station stops, the desired speed of approach of the trains, and in particular the designed braking characteristics of the trains in use. Three stations are shown located along this stretch, designated by the references A, B, and C, from right to left, respectively, the conventional block marking such locations schematically designating the position of the station platform at which the trains stop. These three station platforms are associated, respectively, with track sections 1, 4, and 7, as is obvious from the inspection of the drawing but do not necessarily match the complete section length. It is further assumed that each trains stops at each station along this stretch although, of course, this also is not a specific requirement for the operation of the disclosed system.

The track sections may be separated at the location of the conventional dotted lines by insulated joints. Preferably, however, and herein assumed, the track circuits are of the AF overlay type and therefore insulated joints are not required for proper operation of the track circuits.

As. will be later discussed, insulated joints will normally be used between the station to station blocks of the cab or speed signaling arrangement. To illustrate this use, a single insulated joint j is shown by conventional symbol in the upper rail at the section division point at the entrance to each station. This joint is positioned to the left, i.e., in advance, of the track connection, from the cab signal transmitter CST, over which cab signal energy is applied to the rails, which will be discussed later. As will 'be well understood, an insulated joint will n-ormally be-placed in each rail but only a single symbol is here used as a conventionalillustration. In the AF track circuits specitically shown, a single transmitter energizes several adjoining track circuits which are formed by the use of a plurality of receivers responsive to that single transmitter. These track circuits in the present system are used for train detection in a manner well known, thus indicating the position of trains within the stretch of track. The AF transmitter for several circuits is located and connected across the rails at the entrance of each wayside station. Such transmitters are shown by a conventional solid line b'ock designated as a track circuit or deector transmitter DT, each reference having a suffix to denote the output frequency, for example, X, Y, or Z. Thus the AF transmitter associated with station B, and connected across the rails at the junction of sections 3 and 4, is designated by the reference DTY. The use of the different frequencies eliminates interference between adjoining and/or overlaid track circuits. It is known that a rotation of three different frequencies in such track circuits achieves separation without the use of insulated joints. Each such transmitter DT is connected across the rails as indicated by the previously mentioned dotted lines and is so connected as to feed its output current in both ways into the stretch of track. If insulated joints are used to separate the cab signal circuits in adjoining blocks, as is discussed later, each transmitter DT must be connected across the rails on both sides of such insulated joints in order to achieve both direction transmission of its energy. Such use of insulated joints -between the adjoining station to station blocks does reduce the absolute requirement for different AF track circuit frequencies to a total of two if the availability of different frequencies is critical.

The track circuit receivers are illustrated conventionally by circular symbols, as designated by the note on the drawing, to distinguish from the corresponding track circuit transmitter symbol. The receiver symbols are designated by the reference R plus a letter sux showing the frequency to which that particular receiving unit is responsive. An additional numerical suix designates the track section or sections for which that receiver detects train occupancy. For example, the track circuit receiver located at the junction of sections 2 and 3 is designated as receiver RY3 indicating that it is responsive to frequency Y and detects train occupancy in section 3. In a similar manner, one receiver connected at the junction of sections 1 and 2 is designated by the reference RY2-3, again designating that it is responsive to frequency Y and that it detects occupancy in sections 2 and 3. At the far right associated with the entrance end of the station to station block is receiver RY1-2-3, the numbers again indicating that it detects occupancy of all three track sections within that particular station to station block from station A to station B. In each case where a receiver detects occupancy of more than one section, the rst number in the suix designates the track section detection for which that receiver is primarily used in the system operation. Each track receiver is connected across the rails as indicated by the conventional dotted line, there being no insulated joints in the system using AF track circuits except at the block separation locations. It is to be noted that the most distant receiver in the approach block associated with each transmitter is connected at the same location as the next track circuit transmitter DT, and is connected on its own transmitters side of the insulated joints at that location. Further, at some locations receivers responsive to dilerent frequencies are connected in multiple across the rails at the same point, an example being receivers RX1 and RY2-3 between sections 1 and 2.

The cab signal or speed signal transmitters are shown conventionally by triangular symbols so designated by notes on the drawing and further designated by the reference CST, each with a suffix in accordance with the associated wayside station A, B, or C. Each such cab signal transmitter is connected across the rails as shown by the dotted line convention in multiple with the associated detector transmitter DT. The output of all transmitters CST is at the same frequency in order to be compatible with the train carried apparatus, which responds inductively to the output of these transmitters carried in the rails. Therefore, it is necessary to avoid interference between the different cab signal blocks. One practicable method is to separate adjoining station to station blocks by insulated joints, as shown conventionally in the drawings. Other circuit arrangements are possible, e.g., approach control of these transmitters, which also eliminate any interference and the use of such is included in the scope of the present disclosure. However, in the presently shown system, use of insulated joints is assumed. Each transmitter CST is therefore connected across the rails at the exit end of the approach block to that wayside station, i.e., on the approach side of the insulated rail joints. For example, transmitter CSTB is actually connected across the rails to feed its output toward the approach block which includes track sections 1, 2, and 3.

The output of each transmitter CST is selectively modulated to establish a specic speed signal for transmission to an approaching train. This modulation may be accomplished in several known ways. For example, the well known frequency code system may be used which utilizes pulses of the signaling current at selected rates on the order of 75 to 240 cycles per minute. The train carried apparatus then decodes the received rate to determine the signal to be displayed or the speed limit to be enforced. Other methods of modulation to accomplish the same purpose of selecting and enforcing a speciiic speed limit may be used and such are included within the scope of this disclosure.

The selection of the modulation or coding rate for each transmitter CST is controlled, over conventionally indicated circuit connections, by an associated speed selection logic circuit unit shown by a conventional block so labeled. Each selection logic circuit unit is further designated by a reference SSL with a suffix the same as the associated cab signal transmitter unit CST. For eX- ample, speed selection logic circuits unit SSLB is associated with cab signal transmitter CSTB, the control connections being conventionally shown by the lead designated by reference 13. The logic circuitry within each unit SSL is not specically shown because it is not a unique part of my invention. Such circuitry may be either solid state or relay type but in either case must have failsafe characteristics of a quality normally associated with railway signaling apparatus. The subsequent operational description will indicate to those skilled in the signalling art how such circuitry must function and thus the specific details which must be included in either type of circuit arrangement for a speciiic installation. An example of the general type of relay logic circuitry which may be used is found in the Baughman Patent 3,309,516 issued Mar. 14, 1967, with particular reference to FIG. 5 thereof. Other typical examples of relay contact logic` circuit matrices for controlling the application of cab signal energy are shown in the Allison Patent 2,269,238, Jan. 6, 1942, and the Nicholson et al. Patent 2,331,134, Octf'S, 1943.

Each unit SSL is controlled by the track circuit receivers R located both in approach and in advance of the specific unit. As specifically shown, this control is accomplished over line wires by contacts responsive to the operation of the receivers. These contacts are shown conventionally as relay contacts located immediately below the receiver to which they are responsive. One manner of control is by a receiver relay responsive to the energization and deenergization of the track circuit receiver and such control is here assumed for this specific description. In such operation, the receiver relay picks up to close front contacts when the receivers are energized over the track circuits, that is, no train is occupying the stretch of track between that receiver and its corresponding track circuit transmitter. Such relays release to open their front contacts and close back contacts when no track circuit energy is being received, thus indicating that a train is occupying the track between that' receiver and its transmitter. It is to be noted, and such is included in the scope of this disclosure, that it is possible to provide control energy, responsive to the energization of the track circuit receivers, to the speed selection logic circuits in other ways which will become apparent as speciiic installations are designed by those skilled in the art.

Each cab signal transmitter CST also has connections which are completed under selected conditions to wire loops laid along the rails within the station platform areas and in the immediate approach thereto. In other Words, these loops are laid primarily within sections 1, 4, and 7 as shown by the dot-dash symbols parallel to the rails at those locations. As a specic example7 transmitter CSTB has a second output connection completed at these special times to station loop SLB, located parallel to the rails principally within section 4 but also in the immediate approach thereto, that is, at the exit end of section 3. The purpose of these loops and the slight overlap into the station approach section will be explained later during the operational description. Similar loops SLA and SLC exist at stations A and C, respectively, that is, wilhin section 1 and its approach and within section 7 and its immediate approach in section 6.

The contact matrix responsive to the receivers R controls the units SSLB to achieve the speed selection control shown in FIG. 3. The chart of FIG. 3 illustrates the speed selections for a following train as it moves through the block between stations A and B, hereafter designated as block A-B. Across the top of this chart is a single line schematic illustration of the track stretch of FIG. 1, divided by conventional symbols into the sections 1 to 7 in accordance with the arrangement shown also in FIG. 1. The cab signal transmitters CST are also shown associated with this schematic track diagram to assist in visualizing the various block junction locations. The horizontal lines below the track symbol represent different occupancy conditions, two trains being illustrated in each condition. These trains are shown by conventional symbols, the preceding or lead train being designated by the reference L, shown within the conventional symbol, and the second or following train by the reference F, also shown within the conventional train symbol. The location of each of these trains, under each condition enumerated at the far left of the chart, may be obtained by reference vertically to the track sketch at the top of the chart, the location being designated by the section occupied by that train.

The numerical gure associated with each symbol designating the following train F under the various conditions is the speed limit signal in miles per hour provided by cab signal transmitter CSTB through the rails to that train. In addition, as will be described, station loop SLB shown in condition 3 receives a speed signal for l5 m.p.h. when the special conditions exist under which energy is supplied thereto. The various speed selections have been arbitrarily chosen to illustrate a three indication, speed control system with a high speed of m.p.h., an approach speed of 45 m.p.h., and a STOP signal. The station entering signal of m.p.h. within loop SLB is in addition to the conventional three speeds. Such a system requires three modulation or code rates for the cab signal energy in the rails and loop with the STOP signal being a condition of no energy in the rails. A STOP condition can also be indicated by a steady energy condition, that is, no modulation of the track energy, but this may also occur under fault conditions and therefore is not desirable for the normal STOP indication. The train apparatus is so designed that a condition of stead).f energy as well as no energy will result in a STOP signal or STOP control for the train when such is received. Other speed limits may be used in accordance with requirements in a specic installation. For example, another common approach speed limit in a three indication system is 30 or 35 m.p.h. As previously indicated, the speed limits are selected in accordance with the designed braking characteristics of the trains in use and the lengths of the various track sections.

I shall now describe the operation of the system embodying my invention as shown in FIG. 1, with reference also to FIG. 3 to complete an understanding of the apparatus. Considering first condition 2 as designated in FIG. 3, the leading train L is stopped at station B, that is, is occupying section 4. Under these conditions, track circuit receivers RY4 and RZ4-5-6 are deenergized and contacts responsive to these receivers are released. This occurs, as is well known, since the wheel and axle units of the train provide a shunt between the rails scthat energy owing, for example, from transmitter DTY into the rails of section 4 is shunted away from receiver RY4 which is thus completely deenergized. In a similar manner, the energy owing in the rails from transmitter DTZ at station C is shunted by the wheels and axles so that it does not reach receiver R24-5 5. With train F occupying either section 2 or section 1, receivers RY23 and/or RY1-2-3 are deenergized in a similar manner. It is to be noted that, if train F is in section 1', receiver RXl is also deenergized but this is immaterial to the present description and will be ignored. Receiver RY3 remains energized from the output of transmitter DTY since track section 3 is not occupied. Therefore contact 23 remains picked up, that is, closed as shown in FIG. l. A

Energy is then received by unit SSLB over the line wire controlled by contact 23, bnt not over the line wires controlled by contacts 24 and 25 if train F is in section 2, or energy may be received over the wire line controlled by contact 24 if train. F is oniy in section 1. The circuit network including contacts 21 and 22, controlled by the receivers responsive to the occupancy of section 4, is interrupted at contact 21 `which is released and thus open, so that no energy is received by unit SSLB from the advance block circuits. Under these conditions of track occupancy as detected, that is, track section 4 occupied, track section 3 not occupied, and either track section 2 or 1 occupied, the logic circuits of unit SSLB select a control for transmitter CSTB over lead 13 to actuate the transmission of cab signal current modulated at the approach speed code rate into the rails of block A-B. This cab signal or speed signal current is transmitted through the rails of clock A-B to train F to actuate a response by its train carried equipment to establish a speed limit or signal of 45 m.p.h. for that train.

When train F enters section 3, as in condition 1 in chart 3, receiver RY3 is also deenergized so that its contact 23 releases, thus interrupting the supply of energy over that contact. This removes the supply of all energy from unit SSLB inputs so that the logic circuits are activated to select a new speed limit, under these conditions, the STOP limit. Transmitter CSTB is again controlled and now interrupts any output into the rails of block A-B. With no signalling current in the block, train F picks up no signal which situation is interpreted by its apparatus as a STOP signal and a braking condition to bring the train to a stop is actuated, either manually by the operator or automatically depending upon the type of control system in use. Section 3 is of suicient length to allow the train to come to a complete stop from the approach speed of 45 m.p.h. prior to its arrival at the exit from the section, that is, prior to its entry into section 4 and thus into station B where the preceding train L is or may be standing. This 1tength of section 3 is chosen in keeping with the known braking characteristics designed into the train equipment so that such braking action and the stop of the train can Ebe accomplished in the proper fashion.

With train F now stopped in section 3, train L starts up, ieaves the station area, and clears section 4. Receiver RY4 is now energized since the shunt is removed from the lrails in section 4, and contact 21 picks up and closes. It is to be noted that receiver RZ4-5-6 remains deeners gized, however, since the train shunt still exists across the rails between this receiver and its source of energy, transmitter DTZ. Energy is now applied to unit SSLB over the special circuit including front contact 21 closed and back contact 22 closed, that is, this contact arm in its released position. Contact 23 remains open so that no energy is applied to the right side of unit SSLB. The logic circuits are now actuated to exercise control of transmitter CSTB to complete the special connection to station loop SLB and apply thereto current at the special modulation or code rate to allow a station entry by train F. With train F standing over one end of loop SLB, the signal is received just as though it were received from current in the rails and the cab signal apparatus of the train is actuated to authorize entry into station B. As shown in FIG. 3, this is a low speed on the order of 15 m.p.h. If desired, receiver RY4 may be connected within the limits of section 4 so that contact 21 closes to authorize this slow speed approach into the station platform prior to the time that train L completely clears section 4. If this modied arrangement is used, an additional detection circuit controlled by another RY receiver, connected at the junction of sections 4 and 5 similar to that shown for receiver RY4, will be necessary to supply energy to unit SSLB only when section 4 is completely clear, in order that control circuits for condition 3, which will be discussed next, may be completely set up. Itis to be noted that the special station entering arrangement just described, although shown in the chart of FIG. 3 on the same line as condition 3, is not part of the basic condition controls indicated by the train positions but merely a special entry signal to expedite the movement of train F into the station.

As shown in FIG. 3, condition 3, that is, train L in section 5 or 6, provides for continued transmission of approach speed signals to train F until its exit from block A-B. Separate from this arrangement, a reduction in the speed of train F by its operator or by some automatic arrangement is required in order to allow for a stop at station B. However, this is extraneous to the operation of the signaling system since there is sufficient space between trains F and L to allow the following train to come to a complete stop from the approach speed within section 4, whichris on the safe side. Described specifically, with train L in section 5 or 6, only receiver RY4 receives energy from its source through the rails in advance of station B so that its contact 21 remains closed. 'This is true since train L maintains its shunt across the rails between transmitter DTZ and the other receivers in block B-C. In other words, although contact 2t is closed, contact 22 remains released so that the special circuit previously discussed remains in effect. On the approach side of station B, the position of train F is detected by receiver RY2-3 being deenergized so that its contact 24 is reieased and thus open. Under these conditions, unit SSLB responds to select an approach speed control for transmitter CSTB. This latter unit modulates its output accordingly to transmit the approach speed signal through the rails to the approaching train F. It is to be noted that this result occurs regardless of whether train F is in section 2 or section 3. In other words, the position of contact 23 is immaterial to the operation of unit SSLB under this condition 3. Unit SSLB also responds to control unit transmitter CSTB to continue its output into station loop SLB. As an alternate arrangement, unit SSLB could vary its response, in accordance with the operations of receivers RY3 and RY2-3, so that train F receives a STOP signal when it enters section 3. Train F would then apply its brakes and decelerate from 45 m.p.h., the approach speed, toward a STOP condition at the exit of section 3. However, when it reaches the portion of loop SLB which overlays section 3, it will receive a slow speed signal and thus continue its operation and forward movement into the station area. The selection of the slow speed under these conditions would depend upon the non-occupancy of section 4 and the occupancy of section 3. To the left of unit SSLB, this means that contact 21 is closed while contact 22 remains in its released position closing its back contact. Contact 23 to the right of unit SSLB is open under these conditions, transmission of the STOP signal by transmitter DTY being initiated when this contact opens as train F enters section 3. This alternate operation for condition 3 might be used on the basis that all trains stop at station B anyway and therefore the deceleration is required in any event. This would also simplify the control of transmitter CSTB to complete its connection to activate loop SLB since no other output would be required into the rails at the same time.

Condition 4 of FIG. 3 finds train L in one of the same two sections as condition 3, but train F occupying section 1. Receivers RY3 and RY2-3 are energized and only receive-r RY1-2-3 is deenergized in the approach block. Contacts 23 and 24 are thus closed while contact 25 is open. When energy signals are applied to unit SSLB over these contact positions and over the circuit including front contact 21 and back contact 22, as in the previously described condition, transmitter CSTB is controlled to provide energy at the high speed code rate to the rails of block A-B. This results, of course, in authority by cab signal or speed control for train F to proceed at high speed (80 m.p.h.) while it is occupying section 1.

Condition 4, of course, obviously changes either to condition 3, which has already been discussed, or to condition 5. In the latter, train L moves out of section 6 into section 7 and all receivers RZ receive energy from transmitter DTZ, since no part of block B-C is now occupied by the train. With receiver RZ 4 5-6 now energized, both contacts 21 and 22 are closed in their picked up position. Unit SSLB responds to this signal to select the control for transmitter CSTB to transmit energy at the high speed code rate into block A-B, providing that there is a train F occupying some portion of this block, that is, section 1, 2, or 3. If no train is occupying block A-B under this condition, so that signal energy is received over the line wires controlled by each of the contacts 23, 24 and 25, unit SSLB so responds that transmitter CSTB provides no output into the rails, that is, a STOP signal, since there is no train approaching to receive any other signal. The control of the other units SSL and transmitters CST in the FIG. l arrangement is equivalent to that just described for logic cicuit unit SSLB and its associated transmitter, differing only in accordance with specific location and the contacts responsive to the different receivers involved.

Referring now to FIG.,2, a second form of the system embodying my invention is shown using the same symbols and the same or equivalent reference characters to those of FIG. l. The operation of the second arrangement is 4similar to that of the first but a slight difference in apparatus and arrangement exists. The second forml requires fewer track circuit receivers R, but more wayside line -wires in order to exercise proper control of speed selection The speed signal or control limit selections possible with the arrangement of FIG. 2 are shown in the chart of FIG.

4 which is drawn in a similar manner to that of FIG. 3. Five speed selections are. provided including the STOP signal in the resulting system. These speed limits shown in FIG. 4 are, of course, for example only and are not fixed as a requirement of the arrangement. Although not shown, this second form may also include the station loops, as in FIG. l, in order to provide authorization for a following train to enter the station immediately behind a departing train. Briefly describing the apparatus arrangement, there are no track circuit receivers collocated with the track circuit transmitters DT, which is different from the arrangement of FIG. 1. However, each track circuit transmitter DT feeds its output energy for detection track circuit purposes to track circuit receivers both in the approach and the advance blocks. For example, transmitter DTY provides energy through the approach sections 2 and 3 for receivers RY3 and RY2-3. Receiver RX1 which is collocated with receiver RY2-3 receives energy from transmitter DTX associated with the location at station A. Transmitter DTY in a similar manner feeds into the advance block to energize receiver RY4 which is connected in multiple across the rails at the junction between sections 4 and 5 with a receiver responsive to the next transmitter in advance. Transmitter DTY thus provides detection for trains occupying sections 2, 3, and 4.

The operation of this second arrangement of the invention will now be described, with reference to FIGS. 2 and 4 to assist an understanding. Referring first to FIG. 4, it is noted that, during conditions 1, 2, and 3, lead train L occupies section 4 or is stopped at station B. Receiver RY4 is thus deenergized since the train shunt intervenes between this receiver and its transmitter sourcel DTY. Contact 33 which is responsive to this receiver is thus released and in its open circuit condition. If the following train F is in section 3, that is, condition 1, receiver RY3 is also deenergzed so that its contact 34 likewise is open. It may be noted that receiver RY2-3 also is deenergized under this condition, but receiver RY3 is the ruling unit since it is occupancy of section 3 that is important. The combination of signals thus applied to unit SSLB, due to the open circuit condition of contacts 33 and 34, results in the control of transmitter CSTB to transmit a STOP signal into the rails, that is, a 11o-energy condition which results in a STOP signal on the train.

If train F occupies section 2, that is, condition 2 exists, receiver RY3 is then energized so that contact 34 is closed. However, receiver RY2-3 is still deenergized, its contact 35 is released, and thus the circuit is open. The combination of contact 34 closed and contact 35 open detects the occupancy of section 2, thus locating the train. Under this condition, the energization of receiver RX1 is not material to the determination of the train position by unit SSLB. Therefore, if another train enters station A under a slow speed loop signal, there will be no interference With the proper selection of a speed signal by unit SSLB and the resulting control of transmitter CSTB. With contacts 33 and 35 open and contact 34 closed to thus locate the trains as shown in condition 2, unit SSLB selects a slow speed control which it applies to transmitter CSTB, which in turn supplies energy to the rails of section 3 modulated for this type of speed signal. As indicated in the chart of FIG. 4, the slow speed signal is authority for train F to move at 15 m.p.h.

With train F occupying section 1, that is, condition 3 existing, receiver RX1 is deenergized but receivers RY3 and RY2-3 are energized from their transmitter source. The combination of contact 36 open and contacts 34 and 35 closed, with contact 33 remaining open, actuates unit SSLB to select the approach speed limit shown as being a speed of 30 m.p.h. Transmitter CSTB is then controlled in the usual fashion to transmit a signal having such a modulation or code rate so that when received by train F, the 30 m.p.h. speed limit signal will result. The specific selection of the l5 and 30 m.p.h. speed limits with train L in section 4 is for the purpose of keeping train F moving although at relatively slow speeds so that train L will have time to complete its station stop activities and depart, thus providing some time spacing between the stopping of the trains at this station. If a closer headway between trains is desired, the system can be rearranged so that the speed signal transmitted by transmitter CSTB under both condition 2 and condition 3 will be that authorized the 30 m.p.h. approach speed.

When train L moves into section and clears section 4, that is, departs from station B, receiver RY4 is again energized, since the shunt in section 4 is removed, and its contact 33 picks up to close the circuit. Receiver RZ6 remains energized so that its contact 31 is closed, but receiver RZ5-6 becomes deenergized with the train shunt in section 5 and its contact 32 releases to open the circuit. With contacts 31 and 33 closed and 32 open, the position of train L is detected as being in section 5. This combination of signals applied to the left hand input circuits actuates logic unit SSLB to select the approach speed for application to approach block A-B. This selection, however, is completed only if a train F is occupying section 1, 2, or 3, that is, if any one of contacts 34, 35, or 36 is open due to the deenergization of its receiver- If no train is occupying any portion of block A-B, a STOP signal is selected. This is a safety feature so that no possible overlap of a cab signal transmission from transmitter CSTB may pass beyond the insulated joints at the location of transmitter CSTA. However, with train F approaching, the approach speed signal is applied by transmitter CSTB to the rails of -block A-B so that train F is authorized to approach at the speed of 30 m.p.h. as indicated in condition 4, allowing one section for braking to a stop beyond the location of transmitter CSTB. Actually, with each train stopping at each station, other controls will override the approach speed so that the train will properly be brought to a halt at the station platform, as was previously mentioned in the rst arrangement.

When train L clears into section 6 so that condition 5 exists, receiver RZ6 is also deenergized so that its corresponding contact is released. With contacts 31 and 32 thus in open circuit condition and contact 33 closed, unit SSLB is actuated to select a medium speed control. This control is applied to transmitter CSTB which, by modulating its output at a preselected medium speed code rate, transmits such a signal through block AB. When received by a train in block A-B, it is authorized to proceed at the medium speed limit of 60 m.p.h., since two sections for stopping beyond transmitter CSTB are now available. Once again, of course, a train scheduled to stop at station B must have an overriding control either by the operator or by some wayside arrangement to assure a station stop in the proper manner. It is obvious also that, if other arrangements are desired, a train occupying section 1 or 2 under condition 4 could be authorized to move at this medium speed of 60 m.p.h. since two track sections would then intervene between train F and the preceding train L in section 5.

, When train L shown in FIG. l clears block B-C, that is, moves into section 7 and clears section 6, receivers RZ6 and RZ5-6 are reenergized so that they pick up their contacts 31 and 32 into the closed circuit condition. With all three contacts 31, 32, and 33 now closed, unit SSLB responds to this application of input signals, which indicates a clear block, to select a high speed or maximum speed limit signal for approaching trains, that is, 80 m.p.h. for any train F occupying block A-B. Transmitter CSTB is correspondingly controlled to transmit such a code rate signal into the rails of block A-B. As previously described, this action occurs only if a train F occupies some portion of A-B, otherwise the STOP signal is selected so that no energy is applied to the rails by transmitter CSTB.

The various arrangements embodying my invention thus provide a speed control system utilizing the braking characteristics of the trains to maintain a close headway between such trains. In other Words, each following train in the system disclosed is authorized to advance at the maximum speed for which a suicient and safe braking distance is available, in accordance with the location detected for the preceding train and in accordance with the known braking characteristics of the trains. These speed limits may be modied, if desired, to lower rates in order to space trains a longer distance apart where such spacing meets the operating requirements of the installation. These results are accomplished with a minimum amount of standard apparatus used in a unique manner by the arrangements embodying my invention.

Having thus described my invention what I claim is:

1. A speed signaling system for a stretch of railroad track traversed by trains having predetermined braking characteristics and provided with apparatus for receiving and recording speed signals from the track rails, comprising in combination,

(a) train detection means with connections to the rails of said stretch for continuously detecting the position of trains moving within said stretch,

(b) transmitter means having the same basic output characteristic at preselected locations along said stretch with connections to said rails for transmitting a single selected speed signal modulated onto said characteristic output to approaching trains,

(c) selection logic means at each of said preselected locations controlled by said detection means along said track in approach and advance of that location for selecting, from a plurality of speed limits preselected in accordance with said braking characteristics, one speed limit for an approaching train in accordance with the detected positions of that approaching train and of the immediately preceding train,

(d) each selection logic means having connections for controlling the associated transmitter means to transmit a speed signal corresponding to said selected speed limit.

2. A speed signaling system as defined in claim 1 in which:

each speed signal transmitted by each transmitter means comprises a carrier current of same frequency and modulated in a distinctive manner in accordance with the single selected speed limit.

3. A speed signaling system as dened in claim 1 or 2 in which:

said train detection means includes audio frequency track circuits each having a single energy source and a plurality of detection elements to divide the track between said preselected locations into a plurality of non-insulated sections in which train occupancy is detected.

4. A speed control system for a stretch of railroad track which is traversed in a single direction by trains having established `braking characteristics which enable speed reductions to desired levels within predetermined distances in accordance with the initial train speed, each train being provided with apparatus for receiving a speed limit signal from the track rails and controlling the train speed in accordance therewith, said speed control system comprising in combination, v

(a) consecutive train detection track circuits in said stretch for continuously detecting the presence of trains occupying corresponding sections of said stretch, each section being of a length predetermined in accordance With the braking characteristics of said trains,

(b) speed signal transmitters at preselected locations along said stretch, each having the same basic output frequency,

(1) each transmitter having connections to the track rails for transmitting modulated onto said basic output a selected one of a plurality of speed limit signals, only to an approaching train occupying said stretch between the corresponding location and the location of the next transmitter in approach,

(2) said speed limit signals being predetermined in accordance wtih said established braking characteristics,

(c) speed signal selection means at each preselected location controlled by the track circuits for selecting a speed limit for transmission to an approaching train in accordance with the detected positions of that train and the next preceding train,

(d) each speed selection means having connections for controlling the associated speed signal transmitter to transmit a speed signal corresponding to the selected speed limit for the approaching train, whereby said approaching train is authorized to move at the maximum allowable speed in accordance with the braking distance available between it and the next preceding train.

5. A speed control system as defined in claim 4 in which said track circuits are audio frequency circuits using a plurality of frequencies in a preselected order so that insulated joints separating detector track sections may be eliminated.

6. A speed control system as dened in claim 4 in which said track circuits are audio frequency circuits, a single source supplying detection energy for a selected plurality of adjoining track circuits, each having its own detection means, adjacent sources having different output frequencies so that insulated joints to separate adjoining sections may be eliminated.

7. A speed control system as defined in claim 6, further including a control circuit network for each speed signal selection means controlled by the detection track circuits in approach and in advance of the corresponding location for actuating the associated selection means to select a speed limit for an approaching train in accordance with the detected position of said approaching train and the immediate preceding train.

8. A speed control system as dened in claim 5, 6 or 7 in which each transmitted speed limit signal comprises a carrier current modulated in a distinctive pattern for each selected speed control.

I References Cited UNITED STATES PATENTS 3,337,727 12/ 1963 Freeman 246-63 3,422,262 1/1969 Brockman 246-122 ARTHUR L. LA POINT, Primary Examiner G. H. LIBMAN, Assistant Examiner 

